Inflammatory Mediastinal & Hilar Lymph Nodes
Normal lymph nodes typically do not demonstrate metabolic activity above blood pool background.
It is not uncommon, however, to see significant FDG uptake in otherwise normal mediastinal and bilateral hilar nodes. Very often the distribution of these nodes will be fairly symmetric. Such symmetric uptake is generally considered “reactive or inflammatory in nature.”
Smokers often demonstrate mildly avid mediastinal and hilar lymph nodes, without malignancy.
Occasionally, intensely avid inflammatory mediastinal and hilar nodes can be exceedingly difficult to distinguish from malignancy (e.g. active lymphoma or metastatic adenopathy).
In such cases, we must look for clues to help distinguish inflammation from malignancy. The following inquiries are helpful:
- Is there is bilateral symmetry in node distribution? If so, we favor inflammatory nodes.
- Is there evidence of calcification in some of these nodes? If so, we favor inflammatory etiologies (e.g. granulomatous disease or sarcoidosis).
- Are the nodes enlarged? If so, we are more suspicious of malignancy.
- Is there is a regional primary malignancy (e.g. lung cancer)? If so, we are more suspicious for metastatic nodes.
- Are there nearby malignant nodes (e.g. internal mammary nodes in a breast cancer, or active lymphoma in axillary nodes)? If so, we may favor malignancy.
- Is the primary malignancy distant, and there is no other evidence of metastatic disease? If so, we favor inflammatory nodes (“oncologic plausibility”, discussed here).
While we can confidently distinguish inflammatory nodes from malignant nodes in most cases, there are times when we can only suggest a possible etiology, and are left to “hedge” in our final report.
Case 1
Case 1 (Image 2)
Axial fused images demonstrate the normal PET/CT appearance of the mediastinum and bilateral hila. There are no areas of focal increased FDG uptake to suggest pathology. Uptake within the ascending aorta (“mediastinal blood pool uptake”) is often used as a normal comparative reference value for assessing metabolic activity in the body.
Case 2
Case 2 (Image 2)
Axial images demonstrate hypermetabolic bilateral hilar lymph nodes. They are small (less than a centimeter in the short axis) and fairly symmetric in their distribution.
Case 2 (Image 3)
Axial images demonstrate hypermetabolic mediastinal lymph nodes. They are small (less than a centimeter in the short axis) and fairly symmetric in their distribution. A calcified lymph node is also present, suggesting evidence of prior granulomatous disease. This constellation of findings (small size, symmetry of distribution, and the presence of a calcified node) all suggest that these lymph nodes are inflammatory in nature.
Case 3
Case 3 (Image 2)
Axial images confirm hypermetabolic lymph nodes. They are small (less than a centimeter in the short axis) and fairly symmetric in their distribution. None of these nodes are calcified.
Case 3 (Image 3)
Axial images demonstrate hypermetabolic lymph nodes. They are small (less than a centimeter in the short axis) and fairly symmetric in their distribution, suggesting that all of these lymph nodes are inflammatory in nature — even though they are extremely FDG-avid.
Case 3 (Image 4)
Follow up exam 2-years later demonstrates no significant interval change, confirming that these nodes do not reflect malignancy.
Case 4
Case 4 (Image 2)
Axial images confirm hypermetabolic lymph nodes, fairly symmetric in their distribution. Several are very mildly prominent in size. Several demonstrate areas of faint calcification.
Case 4 (Image 3)
Hypermetabolic mediastinal and bilateral hilar lymph nodes, several of which contain faint calcification. The presence of calcification and their symmetric distribution are highly suggestive of inflammatory lymph nodes.
Case 4 (Image 4)
Hypermetabolic mediastinal and bilateral hilar lymph nodes, several of which contain faint calcification. The presence of calcification and their symmetric distribution are highly suggestive of inflammatory nodes – and are consistent with this patient’s known history of sarcoidosis.
Case 5
Case 5 (Image 2)
Axial images confirm hypermetabolic mediastinal and bilateral hilar lymph nodes, fairly symmetric in distribution. Several nodes are mildly prominent in size. None demonstrate calcification.
Case 5 (Image 3)
Hypermetabolic right paratracheal lymph node, without associated calcification.
Case 5 (Image 4)
Numerous hypermetabolic mediastinal lymph nodes. Although not calcified, their fairly symmetric distribution suggests these are inflammatory in nature (confirmed to be sarcoidosis).
Case 6
Case 6 (Image 2)
Post-therapy exam demonstrates near-complete resolution of these metastatic lymph nodes.
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